Journal of Agricultural Hemp Research Volume 2 Issue 2 Article 1 May 2021 Magnesium’s Impact on Cannabis sativa ‘BaOx’ and ‘Suver Haze’ Growth and Cannabinoid Production Patrick Veazie North Carolina State University Paul Cockson North Carolina State University David Logan North Carolina State University Brian Whipker North Carolina State University Follow this and additional works at: https://digitalcommons.murraystate.edu/jahr Part of the Horticulture Commons Recommended Citation Veazie, Patrick; Cockson, Paul; Logan, David; and Whipker, Brian (2021) "Magnesium’s Impact on Cannabis sativa ‘BaOx’ and ‘Suver Haze’ Growth and Cannabinoid Production," Journal of Agricultural Hemp Research: Vol. 2 : Iss. 2 , Article 1. Available at: https://digitalcommons.murraystate.edu/jahr/vol2/iss2/1 This Journal Article is brought to you for free and open access by Murray State's Digital Commons. It has been accepted for inclusion in Journal of Agricultural Hemp Research by an authorized editor of Murray State's Digital Commons. For more information, please contact [email protected]. Veazie et al.: Impact of Magnesium on Cannabis Sativa Growth and Cannabinoid Production Abstract Limited research exists on the fertility needs for industrial hemp (Cannabis sativa) and the impact of fertility on plant growth and cannabinoids. Optimizing floral production for cannabinoid production and especially cannabidiol (CBD) production, is an economic goal for growers. Magnesium (Mg) is an essential nutrient for plant growth and plays many key roles in plant growth and when deficient leads to suboptimal plant growth. Six Mg fertility rates (0.0, 12.5, 25.0, 50.0, 75.0, and 100.0 mg·L-1) were evaluated to determine the optimal fertility for C. sativa on two High CBD-type cultivars ‘BaOx; and ‘Suver Haze’. Foliar Mg concentrations increased linearly for all life stages with the greatest foliar Mg concentrations being in the highest rate of 100.0 mg·L-1 Mg. Of the six rates, 50.0 and 75.0 mg·L-1 Mg optimized plant height, diameter, and plant total dry weight as well as having similar cannabinoid concentrations during the three life stages. Keywords: hemp, deficiency, macronutrients, nutrition, fertility, fertilizers rates. Published by Murray State's Digital Commons, 2021 1 Journal of Agricultural Hemp Research, Vol. 2, Iss. 2 [2021], Art. 1 Introduction Hemp (Cannabis sativa) has recently gained global popularity and recognition as a viable crop because of the products that contain hemp fibers, oils, and cannabinoids (Salentijn et al., 2019). Hemp, referred to as Cannabis, strains can legally only contain a concentration of tetrahydrocannabinol (THC) of no more than 0.3% of dry weight in any part of the plant (Congress 2014, 2018). Hemp contains cannabidiol (CBD), THC, and over 100 cannabinoids at varying concentrations. Medical and therapeutic benefits are reported by the non-THC cannabinoids, such as CBD, and this has created recent interest in hemp production. Limited published research articles exist on the fertility needs of floral hemp and the impact of fertility on plant growth, total biomass, as well as the production of secondary metabolites such as cannabinoids. A high amount of energy and resources are a requirement for the plant to produce secondary metabolites, such as cannabinoids (Taura et al., 2007). These compounds are typically produced at very low concentrations by the plant (<1% of dry weight) and synthesis is dependent on the plant’s physiological and developmental stage (Akula and Ravishankar, 2011). However, when plants are nutrient stressed, growth (mass) is inhibited to a greater extent than photosynthesis, and thus secondary metabolite concentrations are often increased (Seigler, 1998). Limited research has been conducted on the manipulation of macronutrients and their impact on growth and secondary metabolite production. A higher level of nitrogen (N) increased plant leaf weight and decreased leaf THC concentration in fiber hemp varieties (Bósca et al., 1997). Also, in a THC strain, increasing phosphorus (P) fertilization resulted in a greater bud weight and a higher THC concentration (Coffman, 1997). However, there is limited published research on the impacts of magnesium (Mg) fertility on cannabinoids and other secondary metabolites of hemp grown primarily for floral material. https://digitalcommons.murraystate.edu/jahr/vol2/iss2/1 2 Veazie et al.: Impact of Magnesium on Cannabis Sativa Growth and Cannabinoid Production The economic concern for optimizing cannabinoid production relies on optimizing floral production. As a result, any factor that limits the floral production of hemp, such as fertility level, would be a concern to all growers. It is well known that plants require macro and micronutrients to ensure proper development, growth, and yields. Although many of these essential nutrients for plants are not part of the cannabinoid structure, such as Mg. Magnesium still plays many key roles in plant development and if deficient could result in less plant growth. There are two main reasons for Mg deficiency, absolute deficiency, and cation competition. Absolute deficiency is the result of low Mg content in the soil prior to any fertility treatments this can be caused by Mg losses from the soil by mobilization, leaching, or long-term unbalance crop fertilization practices result in depletion of Mg resources contained within soils (Gransee and Führs, 2013). Cation competition is a consequence of nutrient imbalances in soils. The uptake of + Mg is strongly impacted by the availability of other cations such as ammoniacal-nitrogen (NH4 ), calcium (Ca2+), and potassium (K+) (Fageria, 2001). Thus, growers must monitor these factors to supply a nutritionally balanced fertilizer program and adequate levels of Mg to C. sativa. Within plants, Mg plays many vital roles in plant development. Magnesium is the central atom of the chlorophyll molecule and plays a key role in the ‘light’ and ‘dark’ steps of photosynthesis (Shaul, 2002). However, only one-fifth of leaf Mg is associated with chlorophyll pigments, while up to three-quarters are associated with protein synthesis, with the remainder stored in the vacuole (Verbruggen and Hermans, 2013). Magnesium is also utilized by plants in many ways including RNA polymerase, ATPases, protein kinases, and carboxylases (Shaul, 2002). However, excess Mg in leaf tissue can inhibit photosynthesis and plant growth (Rao et al., 1987). Magnesium is a phloem-mobile element and its remobilization occurs from older leaves to younger ones (Taiz and Zeiger, 2002). Magnesium deficiency disrupts the loading of sucrose into the phloem resulting in Published by Murray State's Digital Commons, 2021 3 Journal of Agricultural Hemp Research, Vol. 2, Iss. 2 [2021], Art. 1 carbon accumulation in the source leaves (Guo et al., 2016). This results in the optimum concentration of Mg in the plant being in the new and developing parts of the plant, such as floral buds (Gransee and Führs, 2013). Magnesium deficiency also impairs root growth which affects the acquisition of water and nutrient uptake (Marschner, 1995). Finding the optimum rate of Mg fertility to promote plant growth is essential to maximize profits for growers. C. sativa plants require Mg for biomass production and secondary metabolites that are essential for growth such as chlorophyll. Leaf Mg concentrations in vegetative mother stock plants prior to when cuttings were harvested were determined in five hemp cultivars (Landis et al. 2019). Plants that appeared healthy and vigorous contained leaf tissue concentrations that ranged from 0.25- 0.46 % Mg (Landis et al., 2019). These values were lower than previously published values of 0.40 and 0.81% Mg (Bryson and Mills, 2014). Other researchers studied the impacts of Mg deficiency on leaf tissue Mg accumulation of C. sativa and reported that plants provided with a modified Hoagland’s solution accumulated 0.61% Mg, while plants grown without Mg contained 0.12% Mg (Cockson et al., 2019). However, there is currently no published literature on optimal Mg fertility rates and their subsequent impact on cannabinoids. The purpose of this study was to investigate the effects of Mg fertilization on the growth and subsequent cannabinoid production of C. sativa. For growers, a fertility rate that maximizes floral yield, biomass, and cannabinoids while minimizing inputs are important. Materials and Methods Two high CBD hemp cultivars ‘BaOx’ and ‘Suver Haze’ (Cannabis sativa) cuttings were obtained from 12-week-old mother stock plants. Terminal vegetative exterior canopy cuttings were taken and stuck on 7 Jan. 2020 into 13-cell foam wedge strips (dimensions: HxWxW (5x3.25x2.5 tapering to 1.5 cm)) (#87-50010, Oasis; Kent, OH). The plants were placed under a mist bench in https://digitalcommons.murraystate.edu/jahr/vol2/iss2/1 4 Veazie et al.: Impact of Magnesium on Cannabis Sativa Growth and Cannabinoid Production a glass greenhouse (35.78 °N latitude with 23.9°C/18.3°C (75 and 65°F) day/night temperatures) and rooted until the first roots appeared on the outside of the plugs (~2 weeks). After root emergence, the plants were irrigated with a nurse solution (33.4 g KNO3, 33.4 g CA(NO3)2 ∙ H2O, 6.6 g KH2PO4, 13.2 g MgSO4 ∙ 7H2O in 20L H2O). After three weeks from sticking, rooted plugs were transplanted on 6 Feb. 2020 into 3.76L plastic pots filled with a custom substrate mix to prevent Mg nutrient contamination that would occur by using a pH adjusted and fertilizer charged commercial substrate. The substrate was a 70:30 (v:v) mix of Canadian sphagnum peat moss (Conrad Fafard, Agawam, MA) and horticultural coarse perlite (Perlite Vermiculite Packaging Industries, North Bloomfield, OH), amended with calcium hydroxide [Ca(OH)2 (Southern Lime, Calera, AL)] at 2.3 kg·m−3 for pH adjustment to 6.0 and wetting agent (AquaGro 2000 G; Aquatrols, Cherry Hill, NJ) at 600 g·m−3. Plants were provided night interruption lighting between 22:00 and 2:00 during the vegetative stage to prevent floral initiation.